3. When do we use a t-statistic instead of a z-statistic to help infer a mean? 4. Identify whether the studies described here are based on (1) single samples, (2) or (3) independent samples. a. Cardiovascular disease risk factors are compared in husbands and wives b. A nutritional exam is applied to a random sample of individuals. Results the results of the whole nation. c. An investigator compares vaccination histories in 30 autistic schoolchild random sample of non-autistic children from the same school district. 5. Identify two graphical methods that can be used to compare quantitative (conti between two independent groups